Make dylib metadata write backend agnostic

Author: bjorn3

Cargo.lock

@@ -14,6 +14,7 @@ crate-type = ["dylib"]
 cranelift = { git = "https://github.com/CraneStation/cranelift.git" }
 cranelift-module = { git = "https://github.com/CraneStation/cranelift.git" }
 cranelift-faerie = { git = "https://github.com/CraneStation/cranelift.git" }
+cranelift-object = { git = "https://github.com/CraneStation/cranelift.git" }
 target-lexicon = "0.8.1"
 faerie = "0.11.0"
 
@@ -28,14 +29,15 @@ libloading = "0.5.1"
 [dependencies.object]
 version = "0.14.0"
 default-features = false
-features = ["compression", "read", "std"] # We don't need WASM support
+features = ["compression", "read", "std", "write"] # We don't need WASM support
 
 # Uncomment to use local checkout of cranelift
 #[patch."https://github.com/CraneStation/cranelift.git"]
 #cranelift = { path = "../cranelift/cranelift-umbrella" }
 #cranelift-module = { path = "../cranelift/cranelift-module" }
 #cranelift-simplejit = { path = "../cranelift/cranelift-simplejit" }
 #cranelift-faerie = { path = "../cranelift/cranelift-faerie" }
+#cranelift-object = { path = "../cranelift/cranelift-object" }
 
 #[patch.crates-io]
 #gimli = { path = "../" }

Cargo.toml

@@ -0,0 +1,48 @@
+pub trait Product {
+    fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, is_like_osx: bool);
+}
+
+impl Product for faerie::Artifact {
+    fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, is_like_osx: bool) {
+        self
+            .declare(".rustc", faerie::Decl::section(faerie::SectionKind::Data))
+            .unwrap();
+        self
+            .define_with_symbols(".rustc", data, {
+                let mut map = std::collections::BTreeMap::new();
+                // FIXME implement faerie elf backend section custom symbols
+                // For MachO this is necessary to prevent the linker from throwing away the .rustc section,
+                // but for ELF it isn't.
+                if is_like_osx {
+                    map.insert(
+                        symbol_name,
+                        0,
+                    );
+                }
+                map
+            })
+            .unwrap();
+    }
+}
+
+impl Product for object::write::Object {
+    fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, is_like_osx: bool) {
+        let segment = self.segment_name(object::write::StandardSegment::Data).to_vec();
+        let section_id = self.add_section(segment, b".rustc".to_vec(), object::SectionKind::Data);
+        let offset = self.append_section_data(section_id, &data, 1);
+        // FIXME implement faerie elf backend section custom symbols
+        // For MachO this is necessary to prevent the linker from throwing away the .rustc section,
+        // but for ELF it isn't.
+        if is_like_osx {
+            self.add_symbol(object::write::Symbol {
+                name: symbol_name.into_bytes(),
+                value: offset,
+                size: data.len() as u64,
+                kind: object::SymbolKind::Data,
+                scope: object::SymbolScope::Compilation,
+                weak: false,
+                section: Some(section_id),
+            });
+        }
+    }
+}

src/backend.rs

@@ -34,6 +34,7 @@ mod allocator;
 mod analyze;
 mod archive;
 mod base;
+mod backend;
 mod cast;
 mod codegen_i128;
 mod common;

src/lib.rs

@@ -9,6 +9,8 @@ use rustc_data_structures::owning_ref::{self, OwningRef};
 use rustc_data_structures::rustc_erase_owner;
 use rustc_target::spec::Target;
 
+use crate::backend::Product;
+
 pub struct CraneliftMetadataLoader;
 
 impl MetadataLoader for CraneliftMetadataLoader {
@@ -51,7 +53,7 @@ impl MetadataLoader for CraneliftMetadataLoader {
 }
 
 // Adapted from https://github.com/rust-lang/rust/blob/da573206f87b5510de4b0ee1a9c044127e409bd3/src/librustc_codegen_llvm/base.rs#L47-L112
-pub fn write_metadata(tcx: TyCtxt<'_>, artifact: &mut faerie::Artifact) -> EncodedMetadata {
+pub fn write_metadata<P: Product>(tcx: TyCtxt<'_>, product: &mut P) -> EncodedMetadata {
     use flate2::write::DeflateEncoder;
     use flate2::Compression;
     use std::io::Write;
@@ -95,24 +97,11 @@ pub fn write_metadata(tcx: TyCtxt<'_>, artifact: &mut faerie::Artifact) -> Encod
         .write_all(&metadata.raw_data)
         .unwrap();
 
-    artifact
-        .declare(".rustc", faerie::Decl::section(faerie::SectionKind::Data))
-        .unwrap();
-    artifact
-        .define_with_symbols(".rustc", compressed, {
-            let mut map = std::collections::BTreeMap::new();
-            // FIXME implement faerie elf backend section custom symbols
-            // For MachO this is necessary to prevent the linker from throwing away the .rustc section,
-            // but for ELF it isn't.
-            if tcx.sess.target.target.options.is_like_osx {
-                map.insert(
-                    rustc::middle::exported_symbols::metadata_symbol_name(tcx),
-                    0,
-                );
-            }
-            map
-        })
-        .unwrap();
+    product.add_rustc_section(
+        rustc::middle::exported_symbols::metadata_symbol_name(tcx),
+        compressed,
+        tcx.sess.target.target.options.is_like_osx,
+    );
 
     metadata
 }